1. Field of the Invention
The present invention relates to a temperature detector in a circuit, and more particularly, to a highly sensitive temperature detector in a circuit.
2. Description of the Related Art
Under certain circumstances, it is important to know the current temperature of an integrated circuit (IC) so as to respond accordingly. For example, a dynamic random access memory (DRAM) requires a refresh action at given times so as to maintain the data stored in the memory cells. The higher the ambient temperature, the more often the refresh action has to be performed because the leakage current of the memory cells is proportional to the ambient temperature. If a DRAM is not installed with a temperature detector, it has to operate at the fastest rate even at a cooler temperature to ensure correct operations, thus wasting power.
U.S. Pat. No. 5,691,661 discloses a pulse signal generating circuit including a ring oscillator and an internal voltage generating circuit. The internal voltage is low at a normal temperature and high at a high temperature. The inverters in the ring oscillator are driven by the internal voltage from the internal voltage generating circuit. As a result, the period of a pulse signal increases at a normal temperature, and decreases at a high temperature. Although U.S. Pat. No. 5,691,661 discloses a temperature detector in DRAM, its temperature-sensing mechanism is not accurate enough to satisfy the need to reduce power consumption in modern IC designs.
US 2006/0140037 A1 discloses an oscillator generating a temperature variable signal that has a frequency proportional to the ambient temperature. By means of a temperature invariant oscillator and an n-bit counter, the ambient temperature can be estimated. In other words, the faster the counter counts, the larger the count value at the end of a sense cycle initiated by the temperature invariant oscillator. A larger count value indicates a warmer temperature, and a smaller count value indicates a colder temperature. The disadvantage of US 2006/0140037 A1 is that the temperature reading is not accurate enough.